1. Field of the Invention
The present invention relates to a PWM signal output circuit.
2. Description of the Related Art
With respect to a motor drive circuit configured to change a current of a motor coil in a gentle manner, the motor drive circuit configured to perform soft switching is known (see, e.g., Japanese Laid-Open Patent Publication No. 2002-186275).
The motor drive circuit configured to perform the soft switching includes a motor drive circuit configured to detect each of a time period during which an FG (Frequency Generator) signal is high and a time period during which the FG signal is low, that is, almost half of the period of the FG signal, and perform the soft switching in the detected time period. Such a motor drive circuit is configured to drive the motor so that a current flowing through the motor coil increases and thereafter decreases in the detected time period, every time a logic level of the FG signal changes.
Incidentally, even if the rotation speed of the motor is constant, since generally the period of the FG signal varies, the time period during which the motor drive circuit increases and thereafter decreases a current flowing through the motor coil might differ from the time period corresponding to half the period of the actual FG signal. Thus, even if the motor is driven to cause a current flowing through the motor coil to increase and thereafter decrease in the detected time period so that a current flowing through the motor coil is sufficiently small at the time of phase switching, as a result, a current flowing through the motor coil is not small at the time of phase switching and the motor may not rotate in a stable manner.